How do you make a knife stabbing effect?

Hi(Bonjour)!

You can animate the knive position and put a mask over it where the blade comes into the leg of the character. The blade's tip will be masked on "entering" the leg.

Michel Boissonneault

Hi(Bonjour) Connor!

Assuming that you master the nesting sequence concept and know how to key out the black portion of the knive clip, here's the tips:

1) put you knive clip in "knive" sequence (ideally, this knive is moving in leg direction or you can even use a knive still with some animation to move them).
2) put you leg clip in "leg" sequence.
3) put you "knive"sequence on V2 in leg sequence (that's the nesting concept).

Play it and your knive should move toward the leg, over the leg clip

To simulate the entering of blade tip in leg:

4) place the playhead where the blade should stop.
5) add a 4 points garbage matte to the "knive" sequence
6) invert the matte and adjust point 1 and 2 of this matte to to "cut" the half bottom portion of the blade.

Now on playing, you should see the knive stabbing the leg.

Add some blood splat still (composited in photoshop in transparent PNG) and voilà.

Michel Boissonneault

Hi(Bonjour)!

Use a color key filter or a 8 points garbage matte (animated) on the knive clip.

Michel Boissonneault

Hi(Bonjour)!

It's a filter. Search the filters with garbage keyword.

By the way, Connor, the user manual in FCE help menu is searcheable too.
There is even an index.

Michel Boissonneault

Hi(Bonjour) Connor!

How did you shoot the knife ?

Is the black background is solid black?

If so, did you try to select a multiply composite mode on the knife clip in timeline ?

Michel Boissonneault